1. Field of the Invention
This invention relates to a golf ball having improved restitution and improved durability in terms of cut resistance and scuff resistance upon iron shots.
2. Prior Art
Golf balls known in the art include one-piece golf balls, solid golf balls, and wound golf balls. The one-piece golf balls are generally prepared by heat curing a rubber composition comprising polybutadiene, methacrylic acid, zinc oxide and peroxide. The solid golf balls including two- and three-piece golf balls are generally prepared by heat curing a rubber composition comprising polybutadiene, zinc acrylate and peroxide to form a solid core and molding a cover around the core with an intermediate layer optionally interposed therebetween. The wound golf balls are generally prepared by molding a cover around a wound core.
Most commonly used as the cover stock in these balls are thermoplastic resins such as ionomer resins and thermoplastic elastomers such as thermoplastic polyester elastomers and polyurethane. The covers formed from thermoplastic resins and thermoplastic elastomers as a main component are resilient, but relatively prone to damage. Especially on iron shots, the covers are readily indented by the club face and scuffed thereby to become fluffy or scraped on the surface.
Then, various proposals have been made for improving the durability of the cover in terms of cut resistance and scuff resistance. For example, JP-A 25867/1982 discloses a cover stock comprising an ionomer resin, an inorganic reinforcement in the form of inorganic glass fibers, and an organic binder. JP-A 311973/1988 discloses a cover stock comprising a synthetic or natural rubber in admixture with surface treated alkali metal titanate fibers. The inorganic glass fibers used in the former do not provide sufficient reinforcement since they are not uniformly dispersible due to their insufficient fiber shape (that is, a low aspect ratio). The inorganic glass fibers rather detract from the resilience of the resin. The alkali metal titanate used in the latter has a low modulus of elasticity and hence, detracts from the resilience of the resin. That is, the alkali metal titanate does not fully satisfy the reinforcement requirement and can deteriorate resin properties.
JP-A 198006/1994 discloses to blend an ionomer resin with needle titanium dioxide. This filler still fails to achieve satisfactory reinforcement.